1. Field of the Invention
The present invention relates to a transmission casing.
2. Description of the Prior Art
It is conventionally known that a processing/assembling hole used for positioning upon a transmission casing being assembled and processed is provided in the transmission casing. Such a reference hole is disclosed in "EC-AT Structure and Service" (Mazda Motor Corporation, Published May, 1985) for example. FIG. 3 shows the conventional structure disclosed in the above publication. A body 01 of the transmission casing has an oil pan mounting flange 03 having an oil pan joint surface 02 for joining the end surface of the oil pan. There is formed a protrusion 04 protruded outwardly on part of the oil pan mounting flange 03, and a processing/assembling hole 05 is formed in the protrusion 04. Further, on the casing body 01 a housing mounting flange 08 having a housing joint surface 07 for joining the end surface of a housing not illustrated in the figure with the transmission casing is formed.
The foregoing conventional transmission casing however has the following difficulties.
Since the conventional transmission casing is constructed such that part of the oil pan mounting flange 03 is protruded, the material cost is increased corresponding to the additional fraction of the protrusion 04, and there is produced the possibility of the protrusion 04 interfering to peripheral instruments to result in the reduced freedom of the design of the transmission casing.
Since the protrusion 04 is flange-shaped, when external force is applied to the protrusion by its being clamped or interfering to other parts upon its being processed or oil pan's being assembled, the protrusion 04 might be deformed to make it difficult for it to be positioned.
There are occasions where a plurality of reinforcing ribs are perpendicularly provided on the outer periphery of a differential gear unit housing 06 of the casing body 01 and further where further reinforcing ribs are provided for supporting the foregoing reinforcing ribs intersecting the same. With such construction, however, a pocket part is sometimes formed on the back side of the further reinforcing ribs. This might cause the possibility of rainwater being collected in the pocket part.